Ken Griffin, the founder and chief executive of $12bn (€9.6bn) hedge fund Citadel Investment Group, has been sued by a former partner for alleged fraud, breach of a partnership agreement and misappropriation of trade secrets.

Rush Simonson, a former business partner of Griffin, claimed in the lawsuit that the hedge fund mogul stole trading software and strategies the two developed for two hedge funds they managed in the 1980s. The proprietary software and strategies have been used to drive Citadel's success, Simonson alleges in the suit.